Switching power converter for direct battery charging

Abstract

A direct charging method is provided that alerts a mobile device when a switching power converter is operating in a constant-current mode to alert the mobile device of an output current without the use of a secondary-side current sense resistor.

We claim: 
     
       1. A method of directly charging a battery for a mobile device using a flyback converter that does not include a sense resistor in series with a secondary winding of a transformer, comprising:
 receiving at a secondary controller for the flyback converter over a data channel in a data interface cable, a desired output voltage command for setting a first output voltage limit and a desired output current command for setting a first output current limit; 
 transmitting the desired output voltage command and the desired output current command from the secondary controller to a primary controller for the flyback converter; 
 in the secondary controller, determining that the primary controller is regulating the cycling of the power switch according to a constant-current mode responsive to a determination by the secondary controller that the output voltage is less than the difference of the first output voltage limit and a voltage margin; and 
 alerting the mobile device of the determination that the primary controller is in the constant-current mode. 
 
     
     
       2. The method of  claim 1 , further comprising:
 responsive to the alerting of the mobile device, receiving a revised output voltage command setting a revised output voltage limit; and 
 regulating the power switch cycling responsive to the revised output voltage limit. 
 
     
     
       3. The method of  claim 2 , wherein the revised output voltage limit is greater than the first output voltage limit. 
     
     
       4. The method of  claim 1 , further comprising:
 digitizing the output voltage to form a digitized output voltage; and 
 from the secondary controller, transmitting the digitized output voltage to the mobile device over the data channel in the data interface cable. 
 
     
     
       5. The method of  claim 4 , further comprising:
 responsive to the digitized output voltage being sufficiently close to the first output voltage limit, transmitting from the mobile device over the data channel in the data interface cable to the secondary controller a revised output current limit command setting a second output current limit that is less than the first output current limit; 
 transmitting the revised output current limit command from the secondary controller to the primary controller; and 
 regulating the cycling of the power switch according to the second output current limit. 
 
     
     
       6. The method of  claim 1 , wherein transmitting the desired output voltage command and the desired output current command from the secondary controller to the primary controller comprises transmitting the desired output voltage command and the desired output current command over an optoisolator. 
     
     
       7. The method of  claim 1 , wherein transmitting the desired output voltage command and the desired output current command from the secondary controller to the primary controller comprises transmitting the desired output voltage command and the desired output current command by pulsing a synchronous rectifier switch. 
     
     
       8. The method of  claim 1 , wherein the data interface cable is a Universal Serial Bus cable. 
     
     
       9. The method of  claim 1 , wherein the data interface cable is a Lightning cable. 
     
     
       10. A flyback converter, comprising:
 a primary controller configured to cycle a power switch in a constant-voltage mode responsive to an output current being less than a first output current limit and to cycle the power switch in a constant-current mode responsive to the output current equaling the first output current limit; and 
 a secondary, controller configured to receive a first output voltage limit and the first output current limit from a mobile device over a data channel in a data interface cable and to transmit the first output voltage limit and the first output current limit to the primary controller, wherein the secondary controller is further configured to transmit a constant-current flag signal to the mobile device responsive to the output voltage being less than a difference of the first output voltage limit and a voltage margin. 
 
     
     
       11. The flyback converter of  claim 10 , wherein the secondary controller is further configured to digitize the output voltage into a digitized output voltage and to transmit the digitized output voltage over the data channel in the data interface cable to the mobile device. 
     
     
       12. The flyback converter of  claim 11 , wherein the data interface cable is a Universal Serial Bus cable. 
     
     
       13. The flyback converter of  claim 11 , wherein the data interface cable is a Lightning cable. 
     
     
       14. The flyback converter of  claim 11 , wherein the secondary controller is further configured to receive a revised output current limit from the mobile device over the data channel in the data interface cable and to transmit the revised output current limit to the primary controller.